Reed switches are used in a variety of devices, including relays of the electromagnetic and electromechanical type, as well as motion and proximity sensors. Reed switches include electrical contacts which are positioned to have a space or gap between them which can be selectively closed and reopened by relative movement of the contacts under the application of a force, such as magnetic or mechanical energy, so as to establish electrical contact between them. The electrical contacts are typically formed into relatively thin, flexible strips or blades of an electrically conductive material.
The responsiveness of the switch is determined in part by the choice of material for the switch contacts and the geometry of the contact blades. Typically the contact blade is made of a nickel/iron alloy and is designed to be sufficiently flexible so that it can move relatively easily under an applied force, such as a magnetic field, yet sufficiently rigid so that it can return to its unloaded orientation.
It is known to reduce the thickness of selected portions of the switch contact blade to enhance the compliance or flexibility of the blade and to optimize the magnetic coupling of the blades. This thinning of the blades is typically accomplished by stamping or pressing the blade in the desired areas. However, pressing or stamping can create burrs or other undesirable stress concentration points in the material. In addition, the material in the thinned regions of the blade is compressed and displaced and thus undergoes a change in its grain structure which is characterized by the term "work hardening" or "working". The work hardened regions of the blade are thus prestressed, whereas the unthinned regions of the blade retain the grain structure and stress-strain characteristics of the original unworked blade material and are not similarly stressed. Work hardening of the material causes it to be denser, less ductile, harder and more brittle, and thus less flexible under load. As a result, greater force is required to move a blade which has been work hardened, and a work hardened blade is less responsive and more likely to fail under load than one which has not been work hardened to achieve a desired geometry.
Flexible reed switches are disclosed in, for example, U.S. Pat. Nos. 3,258,557 to Scheepstra et al., 3,283,274 to De Falco, and 3,866,007, 3,893,051 and 3,943,474 to Schlesinger, Jr. et al. These patents describe reed switch contact blades which incorporate one or more relatively thin regions for enhanced flexibility and reduced contact bounce. The blades are rolled between cylindrical presses to be thinned or necked down in the desired regions.
As previously discussed, the rolling process tends to work the material. The thinned regions of these blades exhibit greater hardness, lower ductility and higher densities than are found in the unworked material, and thus the blades made according to these methods may be relatively weak and unreliable.
It would therefore be an advancement in the art of reed switches to provide reed switch blades which exhibit improved flexibility, performance and life characteristics and which are not subject to the undesirable effects of stamping or pressing.